The present disclosure relates to a semiconductor structure, and particularly to field effect transistors including self-aligned epitaxial active region extensions and a method of manufacturing the same.
The gate length of a field effect transistor is determined by the distance between a pair of active region extensions. Typically, a combination of ion implantation and an activation anneal is employed to form active region extensions. The activation anneal is necessary because only electrical dopants located at substitutional sites are effective in providing free electrical charges in a band gap structure. However, the activation anneal also promotes diffusion of the implanted electrical dopants, thereby blurring the p-n junctions between the body region and the active region extensions. As a result, the diffusion of the implanted electrical dopants during the activation anneal has a deleterious effect of increased leakage current and variations in the threshold voltage. Thus, a field effect transistor is desired in which clearly defined p-n junctions are provided between a body region and active region extensions.